A generic type of drive device is already known for example from EP 1 294 991 B2.
A drive device of this type essentially comprises a main drive, a pump transfer gear and a belt transmission. The belt transmission preferably comprises a first pulley, a second pulley and a belt arranged between the pulleys. The main drive drives the pump transfer gear, which has a least one output shaft, with which the first pulley is driven, and a second output shaft, with which a hydraulic pump is driven. The second pulley is preferably connected to a work roll or a milling drum.
In normal operation, the main drive, usually a diesel engine, drives the downstream components and the milling drum rotates at a suitable speed to mill the road surface and at the appropriate torque.
For maintenance purposes, it is desirable to rotate the milling drum at a slower rotational speed and low torque, to be able to drive it at a specific rotational position. For this purpose, the drive device has an auxiliary device, in most cases, a hydraulic motor or an electric motor.
In EP 1 294 991 B2, it is proposed that the auxiliary device should be coupled with the belt transmission via a friction roller. In this case, the friction roller can be coupled with the roller-side pulley. Alternatively, the auxiliary device can be coupled with at least one drive belt. Another alternative is that the auxiliary device is coupled with the belt transmission via a gear wheel. For example, at least one drive belt of the belt transmission can be comprised of a toothed belt, which engages with the gear wheel of the auxiliary device. In another embodiment, the roller-side pulley can have a gear wheel, which engages with the gear wheel of the auxiliary device.
Essentially, this proposed coupling of the auxiliary device mentioned in EP 1 294 991 B2 is limited to components of the belt transmission. The fact is that, for example, the torque transferable by a friction roller is limited and at a too high resistance point, for example, during a blockade of the work roll, the friction roller may slip through and the risk of accident can be reduced.
Nevertheless, such a coupling of the auxiliary device entails some possible disadvantages. For example, the belt transmission is generally susceptible to contamination or splash water or rainwater, thus, for example, the transmission of a constant torque is not ensured or is only inadequately ensured. Moreover, the wear and tear of a friction roller is very high, so, generally speaking, it has to be replaced more often.